Nordstrom announced it will buy HauteLook, a flash sale site, for $180 million in stock plus an additional three-year earnout of up to $90 million depending on performance.

Flash sale sites, sometimes called private sales or online sample sales, offer huge discounts — up to 75% — on items like clothing and travel packages to their members. The goods are usually excess inventory offered up by wholesalers, fashion designers, and retailers. Membership is required to participate, and deals are advertised in email messages. HauteLook has 4 million members.

The acquisition will help Nordstrom compete with other luxury retailers like Neiman Marcus, who have created their own private sales sites. The deal will also help Nordstrom diversify — important for big retailers as more shopping moves online.